Corona-free top cap terminal assembly for electron discharge devices

ABSTRACT

An electron discharge tube having a corona-free top cap terminal assembly comprising a metallic top cap conductively bonded to the outer surface of the tube envelope.

United States Paten 11 1 1111 3,870,393

Hill Mar. 11, 1975 15 CORONA-FREE TOP CAP TERMINAL 2,446,460 8/1948Dillaby 174/140 2 3,192,610 7/1965 Keating,.. 29 630 ASSEMBLY FORELECTRON DISCHARGE 3,727,088 4/1973 Allgaier 313/178 DEVICES Inventor:Robert L. Hill, Owensboro, Ky.;

Othmar E. Ringeman, St. Meinrod, Ind.

General Electric Company, Owensboro, Ky.

Filed: Feb. 11, 1974 Appl. No.: 441,053

References Cited UNITED STATES PATENTS 3/1943 Victoreen 174/5052 XPrimary Examiner-J. V. Truhue Assistant ExaminerDavid A. Tone Attorney,Agent, or Firm- D. A. Dearing; F. L. Neuhauser {57] ABSTRACT An electrondischarge tube having a coronwfree top cap terminal assembly comprisinga metzillic top cap conductively bonded to the outer surface of the tubeenvelope.

5 Claims, 3 Drawing Figures PATENTEB MAR I 1 I975 FIGJ.

FIGJZB.

HEATING MEANS BACKGROUND OF THE INVENTION This invention relates tomethods and apparatus for manufacturing electrical devices and, moreparticularly, to a method and apparatus for making a top cap terminalassembly for electron discharge tubes.

conventionally, the top cap terminal for high voltage electron dischargetube comprises a cup-shaped metallic member cemented to the top of theglass envelope, for enclosing the tube electrodes, with the rim of thecup-shaped member disposed adjacent the envelope. Viscous fluid, paste,and preformed cements are known types of bonding agents for fixing thetop cap terminal to the envelope. Electrical connection between the topcap and the anode is provided via a lead wire extending through theenvelope which is welded or soldered to an aperture in a top wall of thetop cap. The envelopes for such tube are typically provided with aconductive getter flash or deposit on the inside surface of the envelopeto enhance the vacuum therein. The flash is usually disposed on theinside surface of the envelope pposite the top cap.

Heretofore, such tubes have suffered from the problem that electricalnoise is generated during the use of such devices in televisionreceivers. It was discovered that the primary source of such electricalnoise was a corona or electrical discharge between the rim of the topcap and the envelope 'at points where the rim was spaced from thesurface of the envelope. A secondary source of electrical discharge hasbeen found to be between the anode lead wire and the getter deposit onthe inner surface of the envelope opposite the top cap. This deposit isusually in electrical contact with the lead wire during the early lifeof the tube, but the contact can become broken because the deposit isthin and will deteriorate over the life of the tube.

In addition to the electrical noise created by the corona, it has beenfound that the envelope, which is conventionally made of glass, will beseverely damaged during the life and operation of such devices and canresult in the tube eventually becoming defective.-

The primary source of this problem appears to have been recognized anddiscussed in U.S. Pat. No. 3,727,088 of Allgaier issued on Apr. 10,I973. The Allgaier patent suggests that this source of the problem canbe solved by maintaining the getter assembly at anode potential.

Other solutions which have been suggested are the provision of aconductive paint or coating on the external surface of the envelopeadjacent the rim of the top cap, thereby to provide a conductive pathbetween the top cap rim and the envelope. This was found to eliminatethe corona problem but was found to be unsatisfactory because of theextra cost and labor required to put the conductive paint on thesurface. Furthermore, the paint was found to require careful applicationto prevent the paint from being applied to the surfaces of the top capand envelope to be bonded. If the paint is applied to these surfaces, adefective or weak bond can be produced.

Accordingly, it is an object of this invention to provide an electrondischarge tube with an improved top cap terminal assembly, therebyavoiding the problems associated with the prior art.

It is another object of this invention to provide an electron dischargetube having a top cap terminal assembly conductively bonded to the tubeenvelope.

It is still another object of this invention to provide a top capterminal which can be conductively bonded to the tube envelope in asimple and inexpensive manner. I

Other objects of the invention will be apparent from the followingdescription and accompanying claims.

SUMMARY OF THE INVENTION In accordance with this invention, an electrondischarge tube is provided comprising a tube envelope with aprotuberance thereon, a cup-shaped top cap terminal disposedabout saidprotuberance with the rim of the top cap disposed adjacent the outersurface of said envelope, said top cap being bonded to said envelope byan electrically conductive cement, thereby to provide an electricallyconductive path between said top cap and said envelope.

In accordance with another aspect of the invention, a method forattaching a cup-shaped top cap terminal to an electron discharge tubecomprises providing an electrically conductive cement, disposing saidcement and said cap over an exterior surface of the tube envelope, sothat an electrically conductive bond can be formed between said surfaceand said cap.

The invention will be better understood after consideration of thefollowing description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a view of a fragmentary axialsection of an electron discharge tube with a top cap terminalconstructed in accordance with this invention.

FIGS. 2A and 2B illustrate the steps of attaching a top cap terminal toa tube envelope in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, andmore particularly to FIG. 1, there is shown an electrical element 11,which may be an anode or other electrode, of a sealed discharge devicetube type having a top cap 13 and a lead wire or top cap wire 15projecting from an opening 17 in the top surface of the top cap 13. Thetube type may otherwise be of any conventional construction, such asthat shown and described in U.S. Pat. No. 2,857,544 of .I. F. Stephens,patented Oct. 21, 1958, and assigned to the assignee of thisapplication. The invention, it will be understood, is equally applicableto any other tube type v wherein a top cap terminal or electrodeconnection is required or desired.

The top cap wire 15 fits loosely within the opening 17 of the top cap 13during assembly and fabrication of the tube; and when the fabrication ofthe tube is completed, the top cap wire 15 should be firmly, tightly,and conductively secured to the top cap 13. The cap 13 is a metallic,cup-shaped member of any suitable material, such as brass, and issecured to the envelope 21 of the tube by an electrically conductivecement 19. The cement 19, which, in accordance with this invention,includes a graphite or other conductive particle tiller for goodelectrical conductivity, is preferably any general type of epoxy cementwhich can be preformed in a partially cured, non-tacky state. Suchconductive epoxy cements are well known and are marketed by AmiconCorporation under the trademark Uniset as product No. SE-902-3l.

In FIG. 2A and in accordance with the illustrated embodirnent, thecement 19 is preformed in the shape of an annular ring 25 which can beslid over a protuberance 24 on the outer surface of envelope 21. Afterdisposing the preformed epoxy cement 25 in place, the top cap 13 can bethreaded over the wire with the rim portion 27 thereof ultimatelydisposed adjacent a portion of the outer surface of envelope 21surrounding the protuberance 24. The top cap 13 (FIG. 28) then can beheated by any conventional means 29, such as a gas burner, to soften theannular ring into .a viscous, tacky state so that, upon curing orhardening, an electrically conductive bond is formed between the top caprim 27 and the outer portion of envelope 21. It can be seen that theouter portion of envelope 21 forms acute angle with the rim 27 so thatthe cement 19 can flow in its viscous, tacky state into the taperedspace formed therebetween so as to insure that good electrical contactbetween the rim 27 and the outer portion is formed. Accordingly, it canbe seen that this construction will avoid the corona problems noted insome prior art constructions in a simple and inexpensive manner.

It will be understood by those skilled in the art that the cement neednot be applied in a preformed, nontacky state and further thatconductive cements other than epoxy-based cements can be used within thescope of this invention.

After the top cap 13 has been conductively bonded to the envelope 21,the portion of the wire 15 which extends beyond a projection 25 in theupper portion of the top cap 13 is broken or cutoff. The remainingportion of lead 13 extending into the projection 25 is then welded inaccordance with the method set forth in US. Pat. No. 3,192,610 ofKeating, issued on July 6, 1965, and assigned to the assignee of thisapplication, the disclosure of which is incorporated herein byreference.

Although a particular embodiment of the subject invention has beendescribed, many modifications may be made, and it is understood that theappended claims are intended to cover all such modifications that fallwithin the true spirit and scope of the invention.

What I claim is new and desire to secure by Letters Patent of the UnitedStates is:

1. An electron discharge tube comprising:

a. an evacuated envelopehaving a top wall portion with an externalprotuberance thereon;

b. at least one electrode sealed within said envelope;

c. a lead wire extendingfrom said electrode, said wire passing throughand sealed in said protuberance;

d. a cup-shaped top cap terminal disposed over said protuberance withthe rim of said top cap disposed adjacent an outer surface of said topwall portion, and said top cap electrically connected to said lead; and

e. an electrically conductive cement disposed between said top cap, saidprotuberance, and said surface providing an electrically conductive pathbetween said top cap rim and said surface and bonding said top cap tosaid protuberance and said top wall portion.

2. The tube of claim 1 wherein said cement is a mixture of epoxy andconductive particles.

3. A method for attaching a cup-shaped top cap terminal on an electrondischarge tube, said tube comprising a plurality of electrodes in anenvelope, a lead wire extending from one of said electrodes through saidenvelope and said top cap, said method comprising:

a. providing an electrically conductive cement; and

b. disposing said cement and said cap over .a portion of the exteriorsurface of the envelope through which the lead extends so as to permitthe formation of an electrically conductive bond between said cap andsaid portion.

4. The method of claim 3 wherein said cement is provided in a preformed,non-tacky state, said method fur ther comprising heating said portion,said cement and said cap to form said electrically conductive paththereamong.

5. The method of claim 4 wherein said portion has a protuberance throughwhich said lead extends; said ce' ment is provided in a preformed shapeof an annular ring; and said cement and said cap are disposed aroundsaid protuberance prior to heating. =l

1. An electron discharge tube comprising: a. an evacuated envelopehaving a top wall portion with an external protuberance thereon; b. atleast one electrode sealed within said envelope; c. a lead wireextending from said electrode, said wire passing through and sealed insaid protuberance; d. a cup-shaped top cap terminal disposed over saidprotuberance with the rim of said top cap disposed adjacent an outersurface of said top wall portion, and said top cap electricallyconnected to said lead; and e. an electrically conductive cementdisposed between said top cap, said protuberance, and said surfaceproviding an electrically conductive path between said top cap rim andsaid surface and bonding said top cap to said protuberance and said topwall portion.
 1. An electron discharge tube comprising: a. an evacuatedenvelope having a top wall portion with an external protuberancethereon; b. at least one electrode sealed within said envelope; c. alead wire extending from said electrode, said wire passing through andsealed in said protuberance; d. a cup-shaped top cap terminal disposedover said protuberance with the rim of said top cap disposed adjacent anouter surface of said top wall portion, and said top cap electricallyconnected to said lead; and e. an electrically conductive cementdisposed between said top cap, said protuberance, and said surfaceproviding an electrically conductive path between said top cap rim andsaid surface and bonding said top cap to said protuberance and said topwall portion.
 2. The tube of claim 1 wherein said cement is a mixture ofepoxy and conductive particles.
 3. A method for attaching a cup-shapedtop cap terminal on an electron discharge tube, said tube comprising aplurality of electrodes in an envelope, a lead wire extending from oneof said electrodes through said envelope and said top cap, said methodcomprising: a. providing an electrically conductive cement; and b.disposing said cement and said cap over a portion of the exteriorsurface of the envelope through which the lead extends so as to permitthe formation of an electrically conductive bond between said cap andsaid portion.
 4. The method of claim 3 wherein said cement is providedin a preformed, non-tacky state, said method further comprising heatingsaid portion, said cement and said cap to form said electricallyconductive path thereamong.